Method for monitoring control channel and wireless device

ABSTRACT

A method for monitoring a control channel in a wireless communication system is discussed. The method includes monitoring, by the wireless device, a downlink control channel in a search space of a subframe, wherein the downlink control channel has transmitted based on a localized transmission or a distributed transmission; and receiving, by the wireless device, downlink control information (DCI) via the downlink control channel, wherein the downlink control channel is monitored in at least one enhanced control channel element (ECCE) in a search space, each of the at least one ECCE including a plurality of enhanced resource element groups (EREGs), wherein the plurality of EREGs in each of the at least one ECCE are mapped to one of a plurality of physical resource block (PRB) pairs, for the localized transmission, and wherein the plurality of EREGs are associated with a single antenna port selected from a plurality of antenna ports based on an index of the at least one ECCE and the wireless device&#39;s specific information, for the localized transmission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.15/812,268 filed on Nov. 14, 2017 (now U.S. Pat. No. 10,412,720 issuedon Sep. 10, 2019), which is a Continuation of U.S. patent applicationSer. No. 14/357,122 filed on May 8, 2014 (now U.S. Pat. No. 9,860,884issued on Jan. 2, 2018), which is the National Phase of PCTInternational Application No. PCT/KR2012/009494 filed on Nov. 9, 2012,which claims the priority benefit under 35 U.S.C. § 119(e) to U.S.Provisional Application Nos. 61/663,542 filed on Jun. 23, 2012,61/614,481 filed on Mar. 22, 2012, 61/558,449 filed on Nov. 11, 2011 and61/557,898 filed on Nov. 9, 2011, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method of monitoring a control channel in a wirelesscommunication system, and a wireless device using the method.

Discussion of the Related Art

Long term evolution (LTE) based on 3rd generation partnership project(3GPP) technical specification (TS) release 8 is a promisingnext-generation mobile communication standard. Recently, LTE-advanced(LTE-A) based on 3GPP TS release 10 supporting multiple carriers isunder standardization.

As disclosed in 3GPP TS 36.211 V10.2.0 (2011-06) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 10)”, a physical channel of 3GPP LTE/LTE-A can be classifiedinto a downlink channel, i.e., a physical downlink shared channel(PDSCH) and a physical downlink control channel (PDCCH), and an uplinkchannel, i.e., a physical uplink shared channel (PUSCH) and a physicaluplink control channel (PUCCH).

To cope with increasing data traffic, various techniques are introducedto increase transmission capacity of a mobile communication system. Forexample, a multiple input multiple output (MIMO) technique usingmultiple antennas, a carrier aggregation technique supporting multiplecells, etc., are introduced.

A control channel designed in 3GPP LTE/LTE-A carries a variety ofcontrol information. The introduction of the new technique requires toincrease capacity of the control channel and to improve schedulingflexibility.

SUMMARY OF THE INVENTION

The present invention provides a method of monitoring a downlink controlchannel, and a wireless device using the method.

In an aspect, a method of monitoring a control channel in a wirelesscommunication system is provided. The method includes monitoring, by awireless device, a downlink control channel in a search space that isdefined by at least one physical resource block (PRB) pair, andreceiving, by the wireless device, a downlink grant or an uplink granton the downlink control channel. Each of the at least one PRB pairincludes a plurality of enhanced resource element groups (EREGs). Thesearch space includes a plurality of enhanced control channel elements(ECCEs). Each of the plurality of ECCEs is mapped to at least one EREGaccording to an ECCE-to-EREG mapping scheme. Indexing for the pluralityof ECCEs varies depending on the ECCE-to-EREG mapping scheme.

The ECCE-to-EREG mapping scheme may be one of localized transmission anddistributed transmission. An EREG constituting one ECCE in the localizedtransmission may be transmitted in one PRB pair, and an EREGconstituting one ECCE in the distributed transmission may be transmittedacross a plurality of PRB pairs.

The plurality of ECCEs in the localized transmission may be contiguousin one PRB pair.

In another aspect, a wireless device in a wireless communication systemincludes a radio frequency (RF) unit configured to transmit and receivea radio signal, and a processor operatively coupled to the RF unit andconfigured to monitor a downlink control channel in a search space thatis defined by at least one physical resource block (PRB) pair, andreceive a downlink grant or an uplink grant on the downlink controlchannel.

It is proposed a method of mapping a downlink control channel, in whichblind decoding is performed, to a radio resource.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a downlink (DL) radio frame in 3rdgeneration partnership project (3GPP) long term evolution-advanced(LTE-A).

FIG. 2 is a block diagram showing a structure of a physical downlinkcontrol channel (PDCCH).

FIG. 3 shows an example of monitoring a PDCCH.

FIG. 4 shows an example of arranging a reference signal and a controlchannel in a DL subframe of 3GPP LTE.

FIG. 5 is an example of a subframe having an enhanced PDCCH (EPDCCH).

FIG. 6 shows a physical resource block (PRB) pair structure according toan embodiment of the present invention.

FIG. 7 shows an example of localized transmission and distributedtransmission.

FIG. 8 shows an example of a subset.

FIG. 9 shows an example of blind decoding performed by a wireless devicein each subset.

FIG. 10 shows an example of blind decoding.

FIG. 11 shows an example of EPDCCH monitoring of two wireless devices.

FIG. 12 and FIG. 13 are examples of configuring an aggregation level byusing different subsets at different antenna ports.

FIG. 14 shows an example of configuring an aggregation level.

FIG. 15 shows a subset configured in a PRB pair.

FIG. 16 shows a case where a logical index is assigned to the subset ofFIG. 15.

FIG. 17 shows an example of applying a cyclic shift to the logical indexof FIG. 16.

FIG. 18 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined.

FIG. 19 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined.

FIG. 20 is another example of applying a cyclic shift to the logicalindex of FIG. 16.

FIG. 21 is another example of applying a cyclic shift to the logicalindex of FIG. 16.

FIG. 22 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined based on the logical index ofFIG. 20.

FIG. 23 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined based on the logical index ofFIG. 21.

FIG. 24 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined based on the logical indexof FIG. 20.

FIG. 25 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined based on the logical indexof FIG. 21.

FIG. 26 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined based on the logicalindex of FIG. 20.

FIG. 27 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined based on the logicalindex of FIG. 21.

FIG. 28 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined.

FIG. 29 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined.

FIG. 30 shows an example of configuring a start point of an EPDCCHsearch space.

FIG. 31 shows an example of distributed allocation.

FIG. 32 shows an example of localized allocation.

FIG. 33 shows an example of constructing a distributed enhanced controlchannel element (ECCE) from a localized ECCE.

FIG. 34 is a block diagram showing a wireless communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A wireless device may be fixed or mobile, and may be referred to asanother terminology, such as a user equipment (UE), a mobile station(MS), a mobile terminal (MT), a user terminal (UT), a subscriber station(SS), a personal digital assistant (PDA), a wireless modem, a handhelddevice, etc. The wireless device may also be a device supporting onlydata communication such as a machine-type communication (MTC) device.

A base station (BS) is generally a fixed station that communicates withthe wireless device, and may be referred to as another terminology, suchas an evolved-NodeB (eNB), a base transceiver system (BTS), an accesspoint, etc.

Hereinafter, it is described that the present invention is appliedaccording to a 3rd generation partnership project (3GPP) long termevolution (LTE) based on 3GPP technical specification (TS) release 8 or3GPP LTE-advanced (LTE-A) based on 3GPP TS release 10. However, this isfor exemplary purposes only, and thus the present invention is alsoapplicable to various wireless communication networks. In the followingdescription, LTE and/or LTE-A are collectively referred to as LTE.

The wireless device may be served by a plurality of serving cells. Eachserving cell may be defined with a downlink (DL) component carrier (CC)or a pair of a DL CC and an uplink (UL) CC.

The serving cell may be classified into a primary cell and a secondarycell. The primary cell operates at a primary frequency, and is a celldesignated as the primary cell when an initial network entry process isperformed or when a network re-entry process starts or in a handoverprocess. The primary cell is also called a reference cell. The secondarycell operates at a secondary frequency. The secondary cell may beconfigured after an RRC connection is established, and may be used toprovide an additional radio resource. At least one primary cell isconfigured always. The secondary cell may be added/modified/released byusing higher-layer signaling (e.g., a radio resource control (RRC)message).

A cell index (CI) of the primary cell may be fixed. For example, alowest CI may be designated as the CI of the primary cell. It is assumedhereinafter that the CI of the primary cell is 0 and a CI of thesecondary cell is allocated sequentially starting from 1.

FIG. 1 shows a structure of a DL radio frame in 3GPP LTE-A. The section6 of 3GPP TS 36.211 V10.2.0 (2011-06) “Evolved Universal TerrestrialRadio Access (E-UTRA); Physical Channels and Modulation (Release 10)”may be incorporated herein by reference.

A radio frame includes 10 subframes indexed with 0 to 9. One subframeincludes 2 consecutive slots. A time required for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may have a length of 1 millisecond (ms), and one slot mayhave a length of 0.5 ms.

One slot may include a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain. Since the 3GPP LTE usesorthogonal frequency division multiple access (OFDMA) in a downlink(DL), the OFDM symbol is only for expressing one symbol period in thetime domain, and there is no limitation in multiple access schemes orterminologies. For example, the OFDM symbol may also be referred to asanother terminology such as a single carrier frequency division multipleaccess (SC-FDMA) symbol, a symbol period, etc.

Although it is described that one slot includes 7 OFDM symbols forexample, the number of OFDM symbols included in one slot may varydepending on a length of a cyclic prefix (CP). According to 3GPP TS36.211 V10.2.0, in case of a normal CP, one slot includes 7 OFDMsymbols, and in case of an extended CP, one slot includes 6 OFDMsymbols.

A resource block (RB) is a resource allocation unit, and includes aplurality of subcarriers in one slot. For example, if one slot includes7 OFDM symbols in a time domain and the RB includes 12 subcarriers in afrequency domain, one RB can include 7×12 resource elements (REs).

A DL subframe is divided into a control region and a data region in thetime domain. The control region includes up to first four OFDM symbolsof a first slot in the subframe. However, the number of OFDM symbolsincluded in the control region may vary. A physical downlink controlchannel (PDCCH) and other control channels are allocated to the controlregion, and a physical downlink shared channel (PDSCH) is allocated tothe data region.

As disclosed in 3GPP TS 36.211 V10.2.0, examples of a physical controlchannel in 3GPP LTE/LTE-A include a physical downlink control channel(PDCCH), a physical control format indicator channel (PCFICH), and aphysical hybrid-ARQ indicator channel (PHICH).

The PCFICH transmitted in a first OFDM symbol of the subframe carries acontrol format indicator (CFI) regarding the number of OFDM symbols(i.e., a size of the control region) used for transmission of controlchannels in the subframe. A wireless device first receives the CFI onthe PCFICH, and thereafter monitors the PDCCH.

Unlike the PDCCH, the PCFICH does not use blind decoding, and istransmitted by using a fixed PCFICH resource of the subframe.

The PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink hybridautomatic repeat request (HARD). The ACK/NACK signal for uplink (UL)data on a PUSCH transmitted by the wireless device is transmitted on thePHICH.

A physical broadcast channel (PBCH) is transmitted in first four OFDMsymbols in a second slot of a first subframe of a radio frame. The PBCHcarries system information necessary for communication between thewireless device and a BS. The system information transmitted through thePBCH is referred to as a master information block (MIB). In comparisonthereto, system information transmitted on the PDCCH is referred to as asystem information block (SIB).

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI may include resourceallocation of the PDSCH (this is referred to as a downlink (DL) grant),resource allocation of a PUSCH (this is referred to as an uplink (UL)grant), a set of transmit power control commands for individual UEs inany UE group, and/or activation of a voice over Internet protocol(VoIP).

In 3GPP LTE/LTE-A, transmission of a DL transport block is performed ina pair of the PDCCH and the PDSCH. Transmission of a UL transport blockis performed in a pair of the PDCCH and the PUSCH. For example, thewireless device receives the DL transport block on a PDSCH indicated bythe PDCCH. The wireless device receives a DL resource assignment on thePDCCH by monitoring the PDCCH in a DL subframe. The wireless devicereceives the DL transport block on a PDSCH indicated by the DL resourceassignment.

FIG. 2 is a block diagram showing a structure of a PDCCH.

The 3GPP LTE/LTE-A uses blind decoding for PDCCH detection. The blinddecoding is a scheme in which a desired identifier is de-masked from acyclic redundancy check (CRC) of a received PDCCH (referred to as acandidate PDCCH) to determine whether the PDCCH is its own controlchannel by performing CRC error checking.

A BS determines a PDCCH format according to DCI to be transmitted to awireless device, attaches a CRC to control information, and masks aunique identifier (referred to as a radio network temporary identifier(RNTI)) to the CRC according to an owner or usage of the PDCCH (block210).

If the PDCCH is for a specific wireless device, a unique identifier(e.g., cell-RNTI (C-RNTI)) of the wireless device may be masked to theCRC. Alternatively, if the PDCCH is for a paging message, a pagingindication identifier (e.g., paging-RNTI (P-RNTI)) may be masked to theCRC. If the PDCCH is for system information, a system informationidentifier (e.g., system information-RNTI (SI-RNTI)) may be masked tothe CRC. To indicate a random access response that is a response fortransmission of a random access preamble of the wireless device, arandom access-RNTI (RA-RNTI) may be masked to the CRC. To indicate atransmit power control (TPC) command for a plurality of wirelessdevices, a TPC-RNTI may be masked to the CRC.

When the C-RNTI is used, the PDCCH carries control information for aspecific wireless device (such information is called UE-specific controlinformation), and when other RNTIs are used, the PDCCH carries commoncontrol information received by all or a plurality of wireless devicesin a cell.

The CRC-attached DCI is encoded to generate coded data (block 220).Encoding includes channel encoding and rate matching.

The coded data is modulated to generate modulation symbols (block 230).

The modulation symbols are mapped to physical resource elements (REs)(block 240). The modulation symbols are respectively mapped to the REs.

A control region in a subframe includes a plurality of control channelelements (CCEs). The CCE is a logical allocation unit used to providethe PDCCH with a coding rate depending on a radio channel state, andcorresponds to a plurality of resource element groups (REGs). The REGincludes a plurality of REs. According to an association relation of thenumber of CCEs and the coding rate provided by the CCEs, a PDCCH formatand a possible number of bits of the PDCCH are determined.

One REG includes 4 REs. One CCE includes 9 REGs. The number of CCEs usedto configure one PDCCH may be selected from a set {1, 2, 4, 8}. Eachelement of the set {1, 2, 4, 8} is referred to as a CCE aggregationlevel.

The BS determines the number of CCEs used in transmission of the PDCCHaccording to a channel state. For example, a wireless device having agood DL channel state can use one CCE in PDCCH transmission. A wirelessdevice having a poor DL channel state can use 8 CCEs in PDCCHtransmission.

A control channel consisting of one or more CCEs performs interleavingon an REG basis, and is mapped to a physical resource after performingcyclic shift based on a cell identifier (ID).

FIG. 3 shows an example of monitoring a PDCCH. The section 9 of 3GPP TS36.213 V10.2.0 (2011-06) can be incorporated herein by reference.

The 3GPP LTE uses blind decoding for PDCCH detection. The blind decodingis a scheme in which a desired identifier is de-masked from a CRC of areceived PDCCH (referred to as a candidate PDCCH) to determine whetherthe PDCCH is its own control channel by performing CRC error checking. Awireless device cannot know about a specific position in a controlregion in which its PDCCH is transmitted and about a specific CCEaggregation or DCI format used for PDCCH transmission.

A plurality of PDCCHs can be transmitted in one subframe. The wirelessdevice monitors the plurality of PDCCHs in every subframe. Monitoring isan operation of attempting PDCCH decoding by the wireless deviceaccording to a format of the monitored PDCCH.

The 3GPP LTE uses a search space to reduce a load of blind decoding. Thesearch space can also be called a monitoring set of a CCE for the PDCCH.The wireless device monitors the PDCCH in the search space.

The search space is classified into a common search space and aUE-specific search space. The common search space is a space forsearching for a PDCCH having common control information and consists of16 CCEs indexed with 0 to 15. The common search space supports a PDCCHhaving a CCE aggregation level of {4, 8}. However, a PDCCH (e.g., DCIformats 0, 1A) for carrying UE-specific information can also betransmitted in the common search space. The UE-specific search spacesupports a PDCCH having a CCE aggregation level of {1, 2, 4, 8}.

Table 1 shows the number of PDCCH candidates monitored by the wirelessdevice.

TABLE 1 Number of Search Space Aggregation Size PDCCH Type level L [InCCEs] candidates DCI formats UE-specific 1 6 6 0, 1, 1A,1B, 2 12 6 1D,2, 2A 4 8 2 8 16 2 Common 4 16 4 0, 1A, 1C, 8 16 2 3/3A

A size of the search space is determined by Table 1 above, and a startpoint of the search space is defined differently in the common searchspace and the UE-specific search space. Although a start point of thecommon search space is fixed irrespective of a subframe, a start pointof the UE-specific search space may vary in every subframe according toa UE identifier (e.g., C-RNTI), a CCE aggregation level, and/or a slotnumber in a radio frame. If the start point of the UE-specific searchspace exists in the common search space, the UE-specific search spaceand the common search space may overlap with each other.

In a CCE aggregation level L∈{1,2,3,4}, a search space S^((L)) _(k) isdefined as a set of PDCCH candidates. A CCE corresponding to a PDCCHcandidate m of the search space S^((L)) _(k) is given by Equation 1below.L·{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Herein, i=0,1, . . . , L−1, m=0, . . . , M^((L))−1, and N_(CCE,k)denotes the total number of CCEs that can be used for PDCCH transmissionin a control region of a subframe k. The control region includes a setof CCEs numbered from 0 to N_(CCE,k-1). M^((L)) denotes the number ofPDCCH candidates in a CCE aggregation level L of a given search space.

If a carrier indicator field (CIF) is set to the wireless device,m′=m+M^((L))n_(cif). Herein, n_(cif) is a value of the CIF. If the CIFis not set to the wireless device, m′=m.

In a common search space, Y_(k) is set to 0 with respect to twoaggregation levels L=4 and L=8.

In a UE-specific search space of the aggregation level L, a variableY_(k) is defined by Equation 2 below.Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, A=39827, D=65537, k=floor(n_(s)/2), and n_(s)denotes a slot number in a radio frame.

When the wireless device monitors the PDCCH by using the C-RNTI, asearch space and a DCI format used in monitoring are determinedaccording to a transmission mode of the PDSCH. Table 2 below shows anexample of PDCCH monitoring in which the C-RNTI is set.

TABLE 2 Trans- Transmission mission search mode of PDSCH mode DCI formatspace based on PDCCH Mode 1 DCI format 1A common and Single antennaport, UE specific port 0 DCI format 1 UE specific Single antenna port,port 0 Mode 2 DCI format 1A common and Transmit diversity UE specificDCI format 1 UE specific Transmit diversity Mode 3 DCI format 1A commonand Transmit diversity UE specific DCI format 2A UE specific CDD(CyclicDelay Diversity) or Transmit diversity Mode 4 DCI format 1A common andTransmit diversity UE specific DCI format 2 UE specific Closed-loopspatial multiplexing Mode 5 DCI format 1A common and Transmit diversityUE specific DCI format 1D UE specific MU-MIMO(Multi-user Multiple InputMultiple Output) Mode 6 DCI format 1A common and Transmit diversity UEspecific DCI format 1B UE specific Closed-loop spatial multiplexing Mode7 DCI format 1A common and If the number of UE specific PBCHtransmission ports is 1, single antenna port, port 0, otherwise Transmitdiversity DCI format 1 UE specific Single antenna port, port 5 Mode 8DCI format 1A common and If the number of PBCH UE specific transmissionports is 1, single antenna port, port 0, otherwise, Transmit diversityDCI format 2B UE specific Dual layer transmission (port 7 or 8), orsingle antenna port, port 7 or 8

The usage of the DCI format is classified as shown in Table 3 below.

TABLE 3 DCI format Contents DCI format 0 It is used for PUSCHscheduling. DCI format 1 It is used for scheduling of one PDSCHcodeword. DCI format 1A It is used for compact scheduling and randomaccess process of one PDSCH codeword. DCI format 1B It is used in simplescheduling of one PDSCH codeword having precoding information. DCIformat 1C It is used for very compact scheduling of one PDSCH codeword.DCI format 1D It is used for simple scheduling of one PDSCH codewordhaving precoding and power offset information. DCI format 2 It is usedfor PDSCH scheduling of UEs configured to a closed-loop spatialmultiplexing mode. DCI format 2A It is used for PDSCH scheduling of UEsconfigured to an open-loop spatial multiplexing mode. DCI format 3 It isused for transmission of a TPC command of a PUCCH and a PUSCH having a2-bit power adjustment. DCI format 3 A It is used for transmission of aTPC command of a PUCCH and a PUSCH having a 1-bit power adjustment.

FIG. 4 shows an example of arranging a reference signal and a controlchannel in a DL subframe of 3 GPP LTE.

A control region (or a PDCCH region) includes first three OFDM symbols,and a data region in which a PDSCH is transmitted includes the remainingOFDM symbols.

A PCFICH, a PHICH, and/or a PDCCH are transmitted in the control region.A control format indictor (CFI) of the PCFICH indicates three OFDMsymbols. A region excluding a resource in which the PCFICH and/or thePHICH are transmitted in the control region is a PDCCH region whichmonitors the PDCCH.

Various reference signals are transmitted in the subframe.

A cell-specific reference signal (CRS) may be received by all wirelessdevices in a cell, and is transmitted across a full downlink frequencyband. In FIG. 4, ‘R0’ indicates a resource element (RE) used to transmita CRS for a first antenna port, ‘R1’ indicates an RE used to transmit aCRS for a second antenna port, ‘R2’ indicates an RE used to transmit aCRS for a third antenna port, and ‘R3’ indicates an RE used to transmita CRS for a fourth antenna port.

An RS sequence r_(l,ns)(m) for a CRS is defined as follows.

$\begin{matrix}{{r_{l,{n\; s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\;\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Herein, m=0, 1, . . . , 2N_(maxRB)−1. N_(maxRB) is the maximum number ofRBs. ns is a slot number in a radio frame. l is an OFDM symbol index ina slot.

A pseudo-random sequence c(i) is defined by a length-31 gold sequence asfollows.c(n)=x ₁(n+Nc)+x ₂(n+Nc))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  [Equation 4]

Herein, Nc=1600, and a first m-sequence is initialized as x₁(0)=1,x₁(n)=0, m=1, 2, . . . , 30.

A second m-sequence is initialized as c_(init)=2¹⁰(7(ns+1)+1+1)(2N^(cell) _(ID)+1)+2N^(cell) _(ID)+N_(CP) at a start ofeach OFDM symbol. N^(cell) _(ID) is a physical cell identifier (PCI).N_(CP)=1 in a normal CP case, and N_(CP)=0 in an extended CP case.

A UE-specific reference signal (URS) is transmitted in the subframe.Whereas the CRS is transmitted in the entire region of the subframe, theURS is transmitted in a data region of the subframe and is used todemodulate the PDSCH. In FIG. 4, ‘R5’ indicates an RE used to transmitthe URS. The URS is also called a dedicated reference signal (DRS) or ademodulation reference signal (DM-RS).

The URS is transmitted only in an RB to which a corresponding PDSCH ismapped. Although R5 is indicated in FIG. 4 in addition to a region inwhich the PDSCH is transmitted, this is for indicating a location of anRE to which the URS is mapped.

The URS is used only by a wireless device which receives a correspondingPDSCH. A reference signal (RS) sequence r_(ns)(m) for the URS isequivalent to Equation 3. In this case, m=0, 1, . . . ,12N_(PDSCH,RB)−1, and N_(PDSCH,RB) is the number of RBs used fortransmission of a corresponding PDSCH. A pseudo-random sequencegenerator is initialized as c_(init)=(floor(ns/2)+1)(2N^(cell)_(ID)+1)2¹⁶+n_(RNTI) at a start of each subframe. n_(RNTI) is anidentifier of the wireless device.

The aforementioned initialization method is for a case where the URS istransmitted through the single antenna, and when the URS is transmittedthrough multiple antennas, the pseudo-random sequence generator isinitialized as c_(init)=(floor(ns/2)+1)(2N^(cell) _(ID)+1)2¹⁶+n_(SCID)at a start of each subframe. n_(SCID) is a parameter acquired from a DLgrant (e.g., a DCI format 2B or 2C) related to PDSCH transmission.

The URS supports multiple input multiple output (MIMO) transmission.According to an antenna port or a layer, an RS sequence for the URS maybe spread into a spread sequence as follows.

TABLE 4 Layer [w(0) w(1) w(2) w(3)] 1 [+1 +1 +1 +1] 2 [+1 −1 +1 −1] 3[+1 +1 +1 +1] 4 [+1 −1 +1 −1] 5 [+1 +1 −1 −1] 6 [−1 −1 +1 +1] 7 [+1 −1−1 +1] 8 [−1 +1 +1 −1]

A layer may be defined as an information path which is input to aprecoder. A rank is a non-zero eigenvalue of a MIMO channel matrix, andis equal to the number of layers or the number of spatial streams. Thelayer may correspond to an antenna port for identifying a URS and/or aspread sequence applied to the URS.

Meanwhile, the PDCCH is monitored in an area restricted to the controlregion in the subframe, and a CRS transmitted in a full band is used todemodulate the PDCCH. As a type of control data is diversified and anamount of control data is increased, scheduling flexibility is decreasedwhen using only the existing PDCCH. In addition, in order to decrease anoverhead caused by CRS transmission, an enhanced PDCCH (EPDCCH) isintroduced.

FIG. 5 is an example of a subframe having an EPDCCH.

The subframe may include zero or one PDCCH region 410 and zero or moreEPDCCH regions 420 and 430.

The EPDCCH regions 420 and 430 are regions in which a wireless devicemonitors the EPDCCH. The PDCCH region 410 is located in up to first fourOFDM symbols of the subframe, whereas the EPDCCH regions 420 and 430 maybe flexibly scheduled in an OFDM symbol located after the PDCCH region410.

One or more EPDCCH regions 420 and 430 may be assigned to the wirelessdevice. The wireless device may monitor EPDDCH data in the assignedEPDCCH regions 420 and 430.

The number/location/size of the EPDCCH regions 420 and 430 and/orinformation regarding a subframe for monitoring the EPDCCH may bereported by a BS to the wireless device by using a radio resourcecontrol (RRC) message or the like.

In the PDCCH region 410, a PDCCH may be demodulated on the basis of aCRS. In the EPDCCH regions 420 and 430, instead of the CRS, a DM-RS maybe defined for demodulation of the EPDCCH. An associated DM-RS may betransmitted in the EPDCCH regions 420 and 430.

An RS sequence for the associated DM-RS is equivalent to Equation 3. Inthis case, m=0, 1, . . . , 12N_(RB)−1, and N_(RB) is a maximum number ofRBs. A pseudo-random sequence generator may be initialized asc_(init)=(floor(ns/2)+1)(2N_(EPDCCH,ID)+1)2¹⁶+n_(EPDCCH,SCID) at a startof each subframe. ns is a slot number of a radio frame. N_(EPDCCH,ID) isa cell index related to a corresponding EPDCCH region. n_(EPDCCH,SCID)is a parameter given from higher layer signaling.

Each of the EPDCCH regions 420 and 430 may be used to schedule adifferent cell. For example, an EPDCCH in the EPDCCH region 420 maycarry scheduling information for a primary cell, and an EPDCCH in theEPDCCH region 430 may carry scheduling information for a secondary cell.

When the EPDCCH is transmitted through multiple antennas in the EPDCCHregions 420 and 430, the same precoding as that used in the EPDCCH maybe applied to a DM-RS in the EPDCCH regions 420 and 430.

Comparing with a case where the PDCCH uses a CCE as a transmissionresource unit, a transmission resource unit for the EPDCCH is called anenhanced control channel element (ECCE). An aggregation level may bedefined as a resource unit for monitoring the EPDCCH. For example, when1 ECCE is a minimum resource for the EPDCCH, it may be defined as anaggregation level L={1, 2, 4, 8, 16}.

Hereinafter, an EPDDCH search space may correspond to an EPDCCH region.In the EPDCCH search space, one or more EPDCCH candidates may bemonitored for each one or more aggregation levels.

Now, resource allocation for an EPDCCH will be described.

The EPDCCH is transmitted by using one or more ECCEs. The ECCE includesa plurality of enhanced resource element groups (EREGs). The ECCE mayinclude 4 EREGs or 8 EREGs according to a CP and a subframe type basedon a time division duplex (TDD) DL-UL configuration. For example, theECCE includes 4 EREGs in a normal CP case, and includes 8 EREGs in anextended CP case.

A physical resource block (PRB) pair is 2 PRBs having the same RB numberin one subframe. The PRB pair is a first PRB of a first slot and asecond PRB of a second slot in the same frequency domain. In the normalCP case, the PRB pair includes 12 subcarriers and 14 OFDM symbols, andthus includes 168 resource elements (REs).

An EPDCCH search space may be configured with one or a plurality of PRBpairs. One PRB pair includes 16 EREGs. Therefore, if the ECCE includes 4EREGs, the PRB pair includes 4 ECCEs, and if the ECCE includes 8 EREGs,the PRB pair includes 2 ECCEs.

FIG. 6, including subfigures (A) and (B), shows a PRB pair structureaccording to an embodiment of the present invention. Although it isshown herein that a PRB group includes 4 PRB pairs, there is norestriction in the number of PRB pairs.

The subfigure (A) of FIG. 6 shows an EREG set when an ECCE includes 4RREGs. The subfigure (B) of FIG. 6 shows an EREG set when an ECCEincludes 8 EREGs.

It is assumed hereinafter that the ECCE includes 4 EREGs unlessotherwise specified.

An EPDCCH supports localized transmission and distributed transmission.In the localized transmission, an EREG constituting one ECCE istransmitted in one PRB pair. In the distributed transmission, an EREGconstituting one ECCE is transmitted in a plurality of PRB pairs.

FIG. 7, including subfigures (A) and (B), shows an example of localizedtransmission and distributed transmission. The subfigure (A) of FIG. 7shows an example of ECCE-to-EREG mapping based on localizedtransmission. A localized ECCE is an ECCE used in the localizedtransmission. The subfigure (B) of FIG. 7 shows an example ofECCE-to-EREG mapping based on distributed transmission. A distributedECCE is an ECCE used in the distributed transmission.

An EREG set is a set of EREGs used to construct the localized ECCE orthe distributed ECCE. That is, the ECCE may include EREGs belonging tothe same EREG set.

The EREG set may be generalized to a subset in concept. The subset mayinclude one or more EREGs (or one or more REs) in a PRB pair.

FIG. 8, including subfigures (A) and (B), shows an example of a subset.The subfigure (A) of FIG. 8 shows that a PRB pair includes 4 subsets,and the subfigure (B) of FIG. 8 shows that a PRB includes 4 subsets. APRB of a first slot includes subsets 1, 2, 3, and 4. A PRB of a secondslot includes subsets A, B, C, and D.

When comparing the subset of FIG. 8(A) with the EREG set of FIG. 6(A),one subset may correspond to an EREG set, and may also correspond to oneECCE. When assuming an aggregation level L=1 (i.e., an EPDCCH candidateis monitored in one ECCE), 4 EPDCCH candidates may be monitored in onePRB pair.

It is assumed hereinafter that a subset is included in a PRB pair,unless otherwise specified.

If multiple layers are used, the number of EPDCCHs may vary depending onthe number of antenna ports of a supported DM RS. For example, assumethat there are 4 subsets (i.e., S=4) and 4 antenna ports (i.e., P=4),and thus 4 layers can be supported. In this case, 4 wireless devices canbe spatially multiplexed when considering orthogonality of the DM RS.For example, assume that a wireless device 1 uses an antenna port 1, anda wireless device 2 uses an antenna port 2. A BS indicates the antennaport 1 to the wireless device 1, and transmits an EPDCCH of theaggregation level L=1 to one of the 4 subsets. The wireless device 1detects the EPDCCH by performing blind decoding on each of the 4 subsetscorresponding to the antenna port 1.

FIG. 9 shows an example of blind decoding performed by a wireless devicein each subset.

A BS may report information on a layer and/or an antenna port formonitoring an EPDCCH to the wireless device.

If there are 4 subsets and 4 antenna ports, and if an aggregation levelL=1, then 16 ECCEs can be used throughout all layers. The layer/antennaport may be configured in unit of a wireless device group to effectivelyuse a radio resource. For example, if 4 wireless devices exist inneighboring areas having a similar channel property and thus can formthe same beam or can apply the same precoding, one antenna port can beshared. 4 EPDCCHs for the 4 wireless devices may be transmitted in the 4subsets which exist in the same layer. If the antenna part is shared inthis manner, there is an advantage in that 16 EPDCCHs can be transmittedin one PRB pair through 16 ECCEs.

The following example shows that an antenna port and a subset areallocated to each wireless device in a case where the number of subsetsis S and the number of antenna ports is P. It is assumed that a BSreports an antenna port to each wireless device, and the wireless deviceand the antenna port are 1:1 mapped. The wireless device (WD) performsblind decoding on the subset at a corresponding aggregation level L.Therefore, it can be regarded that whole subsets correspond to an EPDCCHsearch space.

Example 1) S=2, P=4, L=1WD1=antenna port 1+subset 1 or 2WD2=antenna port 2+subset 1 or 2WD3=antenna port 3+subset 1 or 2WD4=antenna port 4+subset 1 or 2

Example 2) S=3, P=4, L=1 or 2WD1=antenna port 1+one (L=1) or two (L=2) subsets among 3 subsetsWD2=antenna port 2+one (L=1) or two (L=2) subsets among 3 subsetsWD3=antenna port 3+one (L=1) or two (L=2) subsets among 3 subsetsWD4=antenna port 4+one (L=1) or two (L=2) subsets among 3 subsets

Example 3) S=4, P=4, L=1, 2 or 4WD1=antenna port 1+one (L=1) or two (L=2) or four (L=4) subsets among 4subsetsWD2=antenna port 2+one (L=1) or two (L=2) or four (L=4) among 4 subsetsWD3=antenna port 3+one (L=1) or two (L=2) or four (L=4) among 4 subsetsWD4=antenna port 4+one (L=1) or two (L=2) or four (L=4) among 4 subsets

FIG. 10 shows an example of blind decoding. Herein, S=4, P=4, and theexample 3 is depicted.

A WD1 receives its EPDCCH in case of using an antenna port 1, L=1, and asubset 2. A WD2 receives its EPDCCH in case of using an antenna port 2,L=2, and subsets 2 and 3. A WD3 receives its EPDCCH in case of using anantenna port 3, L=4, and subsets 1 to 4. A WD4 receives its EPDCCH incase of using an antenna port 4, L=2, and subsets 2 and 4.

An example 4 below shows an antenna port and subset allocation when a DMRS is shared by two wireless devices. When the DM RS is shared, twowireless devices may be allocated to one antenna port. Herein, it isassumed that the DM RS is shared by the WD1 and a WD5, the WD2 and aWD6, the WD3 and a WD7, and the WD4 and a WD8.

Example 4) S=2, P=4, L=1WD1=antenna port 1+subset 1 or 2WD5=antenna port 1+subset 1 or 2WD2=antenna port 2+subset 1 or 2WD6=antenna port 2+subset 1 or 2WD3=antenna port 3+subset 1 or 2WD7=antenna port 3+subset 1 or 2WD4=antenna port 4+subset 1 or 2WD8=antenna port 4+subset 1 or 2

The wireless device monitors the EPDCCH in a PRB pair in a determinedlocation, by using a pre-determined antenna port. Flexible EPDCCHmonitoring is possible by properly assigning an antenna port and/or asubset to a plurality of wireless devices.

FIG. 11, including subfigures (A), (B) and (C), shows an example ofEPDCCH monitoring of two wireless devices.

Referring to the subfigure (A) of FIG. 11, two wireless devices, i.e., aWD1 and a WD2, receive an EPDCCH in different subsets at differentantenna ports. The WD1 receives the EPDCCH in a subset A of an antennaport 1. The WD2 receives the EPDCCH in a subset B of an antenna port 2.

A BS may perform beamforming optimized to each wireless device. Eachwireless device receives the EPDCCH by using orthogonal resources.

Referring to the subfigure (B) of FIG. 11, two wireless devices, i.e., aWD1 and a WD2, receive an EPDCCH in different subsets at the sameantenna port. The WD1 receives the EPDCCH in a subset A of an antennaport 1. The WD2 receives the EPDCCH in a subset B of an antenna port 1.A DM RS may be shared by the WD1 and the WD2, and thus an RS overheadcan be reduced.

Referring to the subfigure (C) of FIG. 11, two wireless devices, i.e., aWD1 and a WD2, receive an EPDCCH in the same subset at different antennaports. The WD1 receives the EPDCCH in a subset A of an antenna port 1.The WD2 receives the EPDCCH in a subset A of an antenna port 2.

A BS is configured to transmit the E-PDCCH by using MU-MIMO. Eachwireless device may be separated by precoding, and thus there is anadvantage in that the number of subsets in use can be decreased.

Now, a case of supporting an aggregation level L (e.g., L=2, 4, 8, 16)higher than L=1 is described.

For example, if it is assumed that the number of subsets is S=2 and thenumber of antenna ports is P=4, a unique resource region may beallocated to the wireless device by using a combination of an antennaport index, a subset index, and a PRB index. Examples of the possiblecombination are as follows.

i) A plurality of subsets are allocated to the same antenna port in alocalized transmission or distributed transmission manner.

ii) The same subset is allocated to different antenna ports in alocalized transmission or distributed transmission manner.

iii) Different subsets are allocated to different antenna ports in alocalized transmission or distributed transmission manner.

FIG. 12 and FIG. 13 are examples of configuring an aggregation level byusing different subsets at different antenna ports. A case of L=1, 2, 4is shown in FIG. 12, and a case of L=8 is shown in FIG. 13.

The proposed method is described above by taking a frequency divisionmultiplexing (FDM)-based subset partitioning for example, and is alsodirectly applicable to time division multiplexing (TDM)-based subsetpartitioning which is achieved on an OFDM symbol basis.

In an example 5 below, an aggregation level is configured by combiningan antenna port, a PRB pair (or PRB), and a subset. Although four PRBpairs (i.e., PRB1, PRB2, PRB3, PRB4) are considered herein, the numberof PRB pairs is for exemplary purposes only.

Example 5) S=4, P=4,L=4 of WD1: Subset 1 of PRB1, Subset 1 of PRB11, Subset1 of PRB3, Subset1 of PRB4L=4 of WD2: Subset 1 of PRB1 2, Subset 2 of PRB2, Subset 2 of PRB3,Subset 2 of PRB4L=4 of WD3: Subset 3 of PRB1, Subset 3 of PRB2, Subset 3 of PRB3, Subset3 of PRB4L=4 of WD4: Subset 4 of PRB1, Subset 4 of PRB2, Subset 4 of PRB3 4,Subset 4o of PRB4

FIG. 14 shows an example of configuring an aggregation level.

In this example, an EPDCCH having an aggregation level L=4 is configuredwith (a subset 1 of PRB1, a subset 1 of PRB2, a subset 1 of PRB3, asubset 1 of PRB4) at the same antenna port, or an EPDCCH having anaggregation level L=4 is configured with (a subset 1 of PRB1, a subset2of PRB2, a subset 3 of PRB3, a subset4 of PRB4) at different antennaports.

Now, a method of configuring a location of an EPDCCH candidate on thebasis of an aggregation level in a search space is described.

FIG. 15 shows a subset configured in a PRB pair.

There are K PRB pairs (i.e., PRB1, . . . , PRB_K), and each PRB pairincludes 4 subsets.

FIG. 16 shows a case where a logical index is assigned to the subset ofFIG. 15. Since there are 4K subsets in K PRB pairs, the logical indexmay be assigned sequentially from 0 to 4K−1.

FIG. 17 shows an example of applying a cyclic shift to the logical indexof FIG. 16. Herein, the logical index for a subset of each PRB pair iscyclically shifted by 2.

Although the same cyclic shift offset is applied for each PRB, this isfor exemplary purposes only. A different cyclic shift offset may beapplied for each PRB. Information on the cyclic shift offset may betransmitted by a BS to a wireless device by using an RRC message or thelike.

FIG. 18 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined.

If L=4, an EPDCCH candidate may be constructed with subsets havingindices 0, 1, 2, and 3 or subsets having indices 4, 5, 6, and 7. If L=8,the EPDCCH candidate may be constructed with subsets having indices 0 to7.

If localized transmission is determined, the aggregation level may beconfigured with a group of subsets having contiguous indices.

In an aggregation level L, a start of a subset for an n^(th) EPDCCHcandidate may be a subset having an index L*(n−1) (n=1, 2, . . . ).Alternatively, if an offset ‘a’ is defined, the start of the subset forthe n^(th) EPDCCH candidate may be a subset having an index L*(n−1)+a.

FIG. 19 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined.

If L=2, an EPDCCH candidate may be constructed with a subsetcorresponding to an index 2 of a PRB1 and a subset corresponding to anindex 6 of a PRB2. If L=4, the EPDCCH candidate may be constructed witha subset corresponding to an index 1 of the PRB1, a subset correspondingto an index 5 of the PRB2, a subset corresponding to an index 9 of aPRB3, and a subset corresponding to an index 13 of a PRB4.

When the distributed transmission is determined, the aggregation levelmay be configured with subsets belonging to different PRB pairs.

FIG. 20 is another example of applying a cyclic shift to the logicalindex of FIG. 16. It is shown herein that the cyclic shift of thelogical index is applied for each PRB pair.

It is shown that a cyclic shift offset 2 is applied to a PRB1, a cyclicshift offset 3 is applied to a PRB2, a cyclic shift offset 0 is appliedto a PRB3, and a cyclic shift offset 1 is applied to a PRB4.

The cyclic shift offset may be reported by a BS to a wireless device.Alternatively, the cyclic shift offset may be determined based on a PRBpair index (or a PRB index). An example of determining a cyclic shiftoffset to (PRB pair index+1) mod 4 is shown in FIG. 20.

FIG. 21 is another example of applying a cyclic shift to the logicalindex of FIG. 16. It is shown herein that the cyclic shift of thelogical index is applied for each group of PRB pairs.

In this example, when it is assumed that a group 1 includes a PRB1 and aPRB2, and a group 2 includes a PRB3 and a PRB4, a cyclic shift offset 2is applied for a PRB pair belonging to the group 1, and a cyclic shiftoffset 1 is applied for a PRB pair belonging to the group 2.

The cyclic shift offset for each group may be reported by a BS to awireless device. The cyclic shift offset for each group may bedetermined based on at least any one of a group index, a PRB pair index,and a PRB index.

FIG. 22 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined based on the logical index ofFIG. 20.

FIG. 23 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined based on the logical index ofFIG. 21.

FIG. 24 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined based on the logical indexof FIG. 20.

FIG. 25 shows an example of a method of configuring an aggregation levelwhen distributed transmission is determined based on the logical indexof FIG. 21.

FIG. 26 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined based on the logicalindex of FIG. 20.

It is assumed that, if L={0, 4, 8}, a start point is a subset having anindex 0.

If L=2, a subset index {0, 4} is selected. If L=4, a subset index {0, 4,8, 12} is selected. If L=8. a subset index {0, 4, 8, 12, 2, 6, 10, 14}is selected.

If a PRB group includes a PRB1, a PRB2, a PRB3, and a PRB4, the subsetindex may be divided into two groups, i.e., {0, 4, 8, 12} and {2, 6, 10,14}. In this case, if L=8, the subset index may be selected such as {0,2, 4, 6, 8, 10, 12, 14}.

FIG. 27 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined based on the logicalindex of FIG. 21.

FIG. 28 shows another example of a method of configuring an aggregationlevel when distributed transmission is determined.

If L=1, a wireless device may sequentially monitor an EPDCCH candidatefor each of 4 subsets corresponding to indices 0, 4, 8, and 12.

If L=2, the wireless device may sequentially monitor the EPDCCHcandidate for each of four subset groups of {0, 8}, {2, 10}, {4, 12},{8,14}.

If L=4, the wireless device may sequentially monitor the EPDCCHcandidate for each of two subset groups {0, 4, 8, 12}, {2, 6, 10, 14}.

If L=8, the wireless device may monitor the EPDCCH candidate for onesubset group {0, 4, 8, 12, 2, 6, 10, 14}.

In the above example, a size and the number of aggregation levels and asubset index corresponding to the aggregation level are for exemplarypurposes only.

If one subset corresponds to one ECCE, one PRB pair may include fourECCEs. According to the exemplary embodiments of FIG. 22 to FIG. 28, ifdistributed transmission is determined, an ECCE for configuring anaggregation level is selected in unit of 4 ECCE indices. Accordingly, ifL=4, the aggregation level is configured with an ECCE having an index{0, 4, 8, 12}.

The wireless device may be required to detect a plurality of EPDCCHs inone PRB pair. For example, the EPDCCH may be determined in each of anECCE having an index 0 and an ECCE having an index 2. For this, aninterval between indices constituting the aggregation level may bedetermined. For example, if an ECCE interval is 4, a first index 0 and anext index 4 are selected and thus EPDCCH candidates exist in differentPRB pairs, whereas if the ECCE interval is 2, a first index 0 and a nextindex 2 are selected and thus two EPDCCH candidates may exist in one PRBpair. Therefore, a BS may send a UL grant by using an ECCE having anindex 0, and may send a DL grant by using an ECCE having an index 2.

To acquire a greater diversity gain, the ECCE interval is preferablygreater than the number of ECCEs included in one PRB pair.

A different ECCE interval may be configured for each aggregation level.For example, if L=1, an ECCE interval may be set to 4, and if L=2, 4, 8,the ECCE interval may be set to 2. The ECCE interval may be determinedbased on the value L.

According to the embodiment of FIG. 28, if L=2, the wireless device maysequentially monitor EPDCCH candidates for 4 ECCE groups {0, 8}, {2,10}, {4, 12}, {8,14}. That is, the ECCE index is increased in the orderof 0, 2, 4, and 6, and may be reconfigured in a direction of increasinga diversity gain, such as 0, 4, 2, and 6.

Although the aggregation level is configured based on an even-numberindex in FIG. 28, the aggregation level may also be configured based onan odd-number index (e.g., 1, 5, 9, 12, etc.). Alternatively, theaggregation level may be configured by combining the odd-number indexand the even-number index (e.g., 0, 2, 5, 9, etc.).

FIG. 29 shows an example of a method of configuring an aggregation levelwhen localized transmission is determined.

If L=1, a wireless device may sequentially monitor EPDCCH candidates foreach of 4 subsets corresponding to indices 0, 4, 8, and 12.

If L=2, the wireless device may sequentially monitor EPDCCH candidatesfor 4 subset groups {0, 1}, {4, 5}, {8, 9}, {12, 13}.

If L=4, the wireless device may sequentially monitor EPDCCH candidatesfor 4 subset groups {0, 1, 2, 3}, {4, 5, 6, 7}, {8, 9, 10, 11}, {12, 13,14, 15}.

If L=8, the wireless device may monitor EPDCCH candidates for 2 subsetgroups {0, 1, 2, 3, 4, 5, 6, 7}, {8, 9, 10, 11, 12, 13, 14, 15}.

The wireless device may receive, from a BS, N PRB pairs for an EPDCCHsearch space and/or information indicating whether to perform localizedtransmission/distributed transmission. In addition, informationregarding an offset for ECCE-to-RE mapping may be received from the BS.The offset may correspond to the cyclic shift offset indicated in theaforementioned embodiment of FIG. 17, FIG. 20, or FIG. 21. The offsetmay depend on the number of subsets (or ECCEs) included in a PRB pair.

FIG. 30 shows an example of configuring a start point of an EPDCCHsearch space.

The start point of the EPDCCH search space may be an index correspondingto a multiple of 4 (e.g., 4A, 4B, 4C, 4D, . . . ) or may be an indexcorresponding to a multiple of 8 (8A, 8B).

FIG. 31 shows an example of distributed allocation. It is assumed hereinthat ECCEs are 1:1 mapped from an index 0 to an index 4N−1. An ECCEindex is mapped in a frequency-first manner.

If L=1, an EPDCCH is mapped to an ECCE having an index 0. If L=2, theEPDCCH is mapped to ECCEs having indices 0 and 1. If L=4, the EPDCCH ismapped to ECCEs having indices 0, 1, 2, and 3. If L=8, the EPDCCH may bemapped across at least 8 PRB pairs. However, although the number of PRBpairs to be allocated is increased when a size of an aggregation levelis increased, the remaining ECCEs other than a corresponding ECCE cannotbe used as a PDSCH. Therefore, if L=8, the EPDCCH may be mapped to 4 PRBpairs in such a manner that 2 ECCEs are mapped to one PRB pair. That is,the EPDCCH may be mapped to ECCEs having indices 0, 1, 2, 3, 2N, 2N+1,2N+2, 2N+3. ‘2N’ may be predetermined, or may be reported by the BS tothe wireless device.

FIG. 32 shows an example of localized allocation. It is assumed hereinthat indices from 0 to 4N−1 of FIG. 30 are 1:1 mapped to ECCEs. An ECCEindex is mapped in a time-first manner. Each PRB pair includes ECCEshaving contiguous indices.

If L=1, 2, 3, an EPDCCH may be mapped to one PRB pair. If L=8, theEPDCCH may be mapped to two PRB pairs.

Although it is assumed in the aforementioned embodiment that a unit ofconfiguring an aggregation level is a subset or an ECCE, this is forexemplary purposes only. 2 ECCEs may be included when L=1. Likewise, 4ECCEs[4 CCE→4 ECCE] may be included when L=2.

The ECCE may include 4 EREGs or 8 EREGs. For example, the ECCE mayinclude 4 EREGs in a normal CP case, and may include 8 EREGs in anextended CP case. To configure an EPDCCH search space, the proposedmethod may be applied to determine how to configure an aggregation levelfrom an ECCE in each PRB pair or whether to designate a start point.

There may be a localized ECCE constructed from an EREG in one single PRBpair and a distributed ECCE constructed from an EREG in a plurality ofPRBs. To ensure a commonality of the EREG index configuring thelocalized ECCE and the EREG index configuring the distributed ECCE, Kdistributed ECCEs may be constructed by re-distributing K localizedECCEs located in different PRB pairs.

FIG. 33 shows an example of constructing a distributed ECCE from alocalized ECCE.

Assume that a PRB pair #m includes 8 RE sets A, B, C, D, E, F, G, and aPRB pair #n includes 8 RE sets A, B, C, D, E, F, G.

If K=2, the RE sets A and E of the PRB pair #m are combined to form alocalized ECCE #a, and the RE sets A and E of the PRB pair #n arecombined to form a localized ECCE #b.

When the distributed ECCE is formed, four RE sets constituting thelocalized ECCE are re-combined. The RE set A of the PRB pair #m and theRE set E of the PRB pair #n may be combined to form the distributed ECCE#a, and the RE set E of the PRB pair #m and the RE set A of the PRB pair#n are combined to form the distributed ECCE #b.

K distributed ECCE indices may be 1:1 mapped to K localized ECCEindices. Therefore, even if the distributed ECCE is transmitted across aplurality of PRB pairs, it may co-exist with the localized ECCE, and anECCE index may be assigned thereto.

FIG. 34 is a block diagram showing a wireless communication systemaccording to an embodiment of the present invention.

ABS 50 includes a processor 51, a memory 52, and a radio frequency (RF)unit 53. The memory 52 is coupled to the processor 51, and stores avariety of information for driving the processor 51. The RF unit 53 iscoupled to the processor 51, and transmits and/or receives a radiosignal. The processor 51 implements the proposed functions, procedures,and/or methods. The processor 51 may configure an EPDCCH search spacefor one or more PRB pairs, and may transmit the EPDCCH.

A wireless device 60 includes a processor 61, a memory 62, and an RFunit 63. The memory 62 is coupled to the processor 61, and stores avariety of information for driving the processor 61. The RF unit 63 iscoupled to the processor 61, and transmits and/or receives a radiosignal. The processor 61 implements the proposed functions, procedures,and/or methods. The processor 61 may monitor an EPDCCH in an EPDCCHsearch space.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for monitoring a control channel in awireless communication system, the method comprising: monitoring, by awireless device, a downlink control channel in a search space of asubframe, wherein the downlink control channel has transmitted based ona localized transmission or a distributed transmission; and receiving,by the wireless device, downlink control information (DCI) via thedownlink control channel, wherein the downlink control channel ismonitored in at least one enhanced control channel element (ECCE) in asearch space, each of the at least one ECCE including a plurality ofenhanced resource element groups (EREGs), wherein the plurality of EREGsin each of the at least one ECCE are mapped to one of a plurality ofphysical resource block (PRB) pairs, for the localized transmission, andwherein the plurality of EREGs are associated with a single antenna portselected from a plurality of antenna ports based on an index of the atleast one ECCE and the wireless device's specific information, for thelocalized transmission.
 2. The method of claim 1, wherein the pluralityof EREGs in each of the at least one ECCE are mapped to the plurality ofthe PRB pairs, and the plurality of EREGs are associated with twoantenna ports of the plurality of antenna ports, for the distributedtransmission.
 3. The method of claim 1, further comprising: receiving,by the wireless device from a base station, information for the searchspace in which the downlink control channel is monitored.
 4. The methodof claim 3, wherein the received information includes first informationrepresenting the plurality of the PRB pairs used for the search space.5. The method of claim 4, wherein each of the plurality of the PRB pairsincludes two PRBs contiguous in the same frequency domain.
 6. The methodof claim 3, wherein the received information further includes secondinformation representing an offset value used for a mapping of thedownlink control channel.
 7. The method of claim 3, wherein the receivedinformation further includes third information representing the subframein which the downlink control channel is monitored.
 8. The method ofclaim 1, wherein the downlink control channel is demodulated by using ademodulation reference signal that is generated based on an identifier.9. The method of claim 1, wherein each of the at least one ECCE includes4 EREGs or 8 EREGs.
 10. The method of claim 1, further comprising:receiving information representing an allocation of the single antennaport to the wireless device.
 11. A wireless device for monitoring acontrol channel in a wireless communication system, the wireless devicecomprising: a transceiver configured to transmit and receive a radiosignal; and a processor operatively coupled to the transceiver andconfigured to: monitor a downlink control channel in a search space of asubframe, wherein the downlink control channel has transmitted based ona localized transmission or a distributed transmission; and control thetransceiver to receive downlink control information (DCI) via thedownlink control channel, wherein the downlink control channel ismonitored in at least one enhanced control channel element (ECCE) in asearch space, each of the at least one ECCE including a plurality ofenhanced resource element groups (EREGs), wherein the plurality of EREGsin each of the at least one ECCE are mapped to one of a plurality ofphysical resource block (PRB) pairs, for the localized transmission, andwherein the plurality of EREGs are associated with a single antenna portselected from a plurality of antenna ports based on an index of the atleast one ECCE and the wireless device's specific information, for thelocalized transmission.
 12. The wireless device of claim 11, wherein theplurality of EREGs in each of the at least one ECCE are mapped to theplurality of the PRB pairs, and the plurality of EREGs are associatedwith two antenna ports of the plurality of antenna ports, for thedistributed transmission.
 13. The wireless device of claim 11, whereinthe processor is further configured to: control the transceiver toreceive information for the search space in which the downlink controlchannel is monitored.
 14. The wireless device of claim 13, wherein thereceived information includes first information representing theplurality of the PRB pairs used for the search space.
 15. The wirelessdevice of claim 14, wherein each of the plurality of the PRB pairsincludes two PRBs contiguous in the same frequency domain.
 16. Thewireless device of claim 13, wherein the received information furtherincludes second information representing an offset value used for amapping of the downlink control channel.
 17. The wireless device ofclaim 13, wherein the received information further includes thirdinformation representing the subframe in which the downlink controlchannel is monitored.
 18. The wireless device of claim 11, wherein thedownlink control channel is demodulated by using a demodulationreference signal that is generated based on an identifier.
 19. Thewireless device of claim 11, wherein each of the at least one ECCEincludes 4 EREGs or 8 EREGs.
 20. The wireless device of claim 11,wherein the processor is further configured to: control the transceiverto receive information representing an allocation of the single antennaport to the wireless device.